A variety of studies of clinical disorders of male reproduction are in progress. These include 1) studies of the hormonal regulation of spermatogenesis in hypogonadotropic men, 2) analysis of biochemical parameters of sperm metabolism in men with non-motile sperm, 3) longitudinal evaluation of the adverse effects of cytotoxic drugs on testicular function in men receiving chemotherapy for malignant disorders, and 4) the evaluation of treatment of men with idiopathic infertility.